A small addition to the C100: It can cause slight electrical noise because it is operated directly via USB. I have a Topping E30 v2 here for testing, which is absolutely quiet. However, with the C100 you can only hear it on high gain and when you turn up the amplifier completely. Even if I need another power supply then, I will probably keep the Topping DAC because (in addition to the non-existent noise) it also switches off automatically when it is not needed.
By the way: the Topping E30 has the same XMOS Chip as the C200 and no clicking noise here. Well (done, Topping!
(EDIT) One more addition: The optical input and coax of the C100 are quite noisy, even when the unit is connected to a good power supply and nothing else is attached. Perhaps one should really be careful with the SMSL C100.